A microcontroller unit (MCU) or other integrated circuit can include internal reference clock (IRC) circuitry that provides a reference clock during a boot cycle of the MCU. The IRC circuitry can include a sequential circuit, and as the output of the sequential circuit toggles, the IRC clock signal provided by the IRC circuitry also toggles. An initial state of the sequential circuit should be defined at the start-up of the IRC circuitry. The initial state of the sequential circuit can be ensured through a reset pin of the flip-flop, which can be a voltage indicator for the power supplies of the IRC circuitry. However, different situations can arise that can cause the IRC circuitry to deadlock or to glitch, and in these situations the IRC clock signal is no longer provided by the IRC circuitry to the MCU or integrated circuit. For example, if the sequential circuit attains a wrong state, then a feedback loop within IRC circuitry can be deadlocked. Another situation is that noise on a power supply voltage provided to the IRC circuitry can also cause the IRC circuitry to deadlock. Further, an asynchronous reset signal can cause a glitch in the output clock signal. Therefore, a component is needed within the IRC circuitry to prevent IRC circuitry deadlocks and glitches.
The use of the same reference symbols in different drawings indicates similar or identical items.